There is increasing evidence to suggest that a flowering hormone exists in plants. This is has been supported by a number of grafting experiments. A short day plant kept in long day conditions can be induced to flower, if a properly photo induced plant is grafted on it. It clearly indicates that a diffusible flowering hormone has moved from one plant to the other and has induced the latter to flower. This hormone has been named florigen but it has so far not been isolated.
Vernalisation prepares a plant to flower. It makes the plant perceptive to a stimulus but does not function as a stimulus.If vernalisation is followed by high temperature treatment at about 40o C for a minimum of 2 days, the vernalisation stimulus is lost. This is known as devernalisation.